Synergistic microbubble ozonation and CaO2 activation for refinery sludge valorization: Organic carbon liberation and petroleum hydrocarbon degradation

Petroleum-containing waste sludge (PWS) accumulation and internal carbon scarcity are major hurdles in oily wastewater treatment. This study develops a cleaner production strategy using microbubble ozonation (MB-O 3 ) coupled with calcium peroxide (CaO 2 ) activation to simultaneously valorize PWS and remediate hydrocarbons. The MB-O 3 /CaO 2 treatment (initial pH 7.0, CaO 2 dosage of 0.25 g/gTS) released 7620 mg/L of soluble chemical oxygen demand (SCOD) and 1163 mg/L of volatile fatty acids (dominated by acetic and propionic acid), improving sludge biodegradability by 6.8-fold. Concurrently, 70.3% total petroleum hydrocarbon (TPH) removal was achieved following pseudo-first-order kinetics, demonstrating broad-spectrum degradation across C 10 -C 40 hydrocarbons. Mechanistic insights reveal that the synergistic effect hinges on the microbubble-enhanced ozone mass transfer and the dual-functional role of CaO 2 in sustained H 2 O 2 liberation and self-driven pH modulation. The transition from •O 2 − dominated alkaline micro-zones to a persistent •OH oxidation regime ensures the synchronous mobilization of entrapped organic carbon and the oxidative cracking of hydrocarbons. Correlation analysis confirms that carbon liberation and TPH removal are mutually reinforcing processes. This strategy facilitates simultaneous waste remediation and carbon liberation, aligning with circular economy principles.